Over the last several years, the Stuttering Foundation has kept accurate data on the calls it has received from concerned parents of 15,374 preschool children who are reported to be stuttering. 
The number of enquiries rises sharply at 3 years of age and then lessens for children aged 4 and then further reduces for children aged 5 years. Note that 19% report onset of stuttering at 5 years old.
Across all ages, we receive more enquiries from parents of boys than we do of girls, reflecting what we know - that more boys stutter than girls (Bloodstein, 1995; Yairi, 2005). 
When we look at the proportion of those children who are male and female, it is interesting to see that the ratio of females:males differs across the ages, with proportionally fewer calls from parents of 5-year old girls compared to 2 year olds. 
Research has found that girls are more likely to recover from stuttering than boys (Yairi, 2005). Our data would seem to lend further support to this.  Dr. Soo-Eun Chang’s ongoing research with preschool children at Michigan State University may shed more light on neurological development during these crucial preschool years.
-August 2013